Seat occupancy sensors are nowadays widely used in automotive vehicles to provide a seat occupancy signal for various appliances, such as, e.g. a seat belt reminder, an auxiliary restraint system (airbag), etc. The possibility of customization and personalization of the vehicle by the customer is a key selling factor of modern cars. This leads to many different variants of car interiors being offered for one car model. With the increasing number of available options, severe constraints arise concerning the implementation of technical equipment in the vehicle. With seat occupancy sensors arranged between the foam body of the seat cushion and the seat cover, every seat design (leather, cloth, sport, comfort, . . . ) requires specific development effort for the occupant detection system. That induces high development costs and therefore is an unattractive solution for the automotive industry. A problem to be solved is, therefore, to find a sensor solution, which is less influenced by seat design and thus can be used for a greater variety of car seats or even car platforms.
Document EP 1 666 311 B1 discloses a vehicle seat assembly comprising a seat support pan, a seat cushion, a spring biased lever and an operator present switch. Both the lever and the switch are located between the cushion and the pan, effectively integrated within the seat. The lever is movable between upper and lower positions, with its associated spring biasing the lever toward its upper position. The switch is designed and located so that all of its components are housed within the support pan and none of these components extends below or outside of the pan. When the seat is occupied, the occupant's weight depresses the cushion and, in turn, the lever moves against the force of the spring toward its lower position and the switch is actuated.
A drawback of the vehicle seat assembly of document EP 1 666 331 resides in the fact that it requires the presence of a seat pan. For comfort reasons, however, modern seats often comprise a suspension mat, instead of a seat pan, to support the seat cushion.